1. Field of the Invention
The present invention relates to a method for separating and purifying 2-t-butyl-4-methylphenol and 2-t-butyl-5-methylphenol from a t-butylcresol mixture.
2. Prior Art
2-t-butyl-4-methylphenol (4M2B) and 2-t-butyl-5-methylphenol (3M6B) are known as important compounds in the filed of agricultural chemicals and the like and are widely used.
For obtaining 4M2B or 3M6B, there is a known method in which m-cresol and p-cresol are previously separated from a m,p-cresol mixture which is industrially easily available, and each isomer is butylated.
Also, a method is known in which a m,p-cresol mixture is dibutylated to obtain a mixture of 2,6-di-t-butyl-4-methylphenol (4M26B) and 4,6-di-t-butyl-3-methylphenol (3M46B), the mixture is separated, then, each isomer is de-monobutylated or transalkylated with cresols.
However, in the former method, m-cresol and p-cresol must be previously separated from a m,p-cresol mixture, and further, after the separated isomers are respectively butylated, 4M2B or 3M6B must be separated and purified again by distillation and the like from the reaction product containing unreacted cresol and a dibutylated by-product compound.
Additionally in the latter method, 4M26B and 3M46B must be previously separated from the dibutylated reaction mixture of a m,p-cresol mixture, and further, after the isomers are respectively de-monobutylated or transalkylated with cresols, 4M2B or 3M6B must be separated and purified again by distillation and the like from the reaction product containing cresols and an unreacted dibutylated compound.
As described above, for obtaining 4M2B and 3M6B in the conventional methods, separation into a m-isomer system and a p-isomer system such as separation into m-cresol and p-cresol in raw materials for butylation reaction of a m,p-cresol mixture or separation into a dibutyl isomer derived from m-cresol and a dibutyl isomer derived from p-cresol after dibutylation reaction has been required.
The reason for this is that it has been supposed to be difficult to separate and purify 4M2B and 3M6B by distillation from such a t-butylcresol mixture since the difference in boiling points of 4M2B and 3M6B (127.degree. C. and 132.degree. C. respectively, each measured at 2.67 KPa) is small, and a de-monobutylated or transalkylated reaction mixture with cresols of a dibutylated reaction mixture of a m,p-cresol mixture or a butylated reaction mixture of a m,p-cresol mixture contains compounds having a lower boiling point than that of 4M2B and compounds having a higher boiling point than that of 3M6B (Industrial and Engineering Chemistry, 35, No. 3, 264 (1943)).
It is industrially advantageous from the viewpoint of operation to separate 4M2B and 3M6B from a t-butylcresol mixture containing 3M6B, 4M2B, compounds having a higher boiling point than that of 3M6B and compounds having a lower boiling point than that of 4M2B obtained by using an industrially easily available m,p-cresol mixture as a raw material without any treatment, and without separation into a m-isomer system and a p-isomer system in its raw material stage, therefore, development of a method for such a separation has been strongly desired.